Heat exchangers frictional loss

Heat exchangers use energy two ways as frictional pressure drop, and as the loss in ability to do work when heat is degraded. 

Heat Exchanger Approach 5°C = 40°F Approx Friction Factor 0.005 (1 velocity head loss every 50-60 length to diameter ratios)... 

Figure 2-43. Evaluation curves for friction losses of air and steam flowing turbulently in commercial pipe at low pressures. By permission, Standards for Steam Jet Ejectors, 4th Ed., Heat Exchange Institute, 1988.

The values of friction loss (including entrance, exit losses, pressure drop through heat exchangers, control valves and the like) are hjL and h L. The total static head is D — Sl, or [(D -f D ) — (—Sl)] if siphon action is ignored, and [(D + D ) — (S l)] for worst case, good design practice. 

The total static head of the system is [D - (-S)] or (D -I-S) and the friction loss is still h L + hjL, which includes the heat exchanger in the system. 

The first two effects are calculated directly from the overall process design. The frictional losses are obtained from the compressor power requirements. They amount to a total exergy destruction of 10 MW. Heat exchanger losses due to heat transfer in Units 1-6 (excluding the reformer) can be evaluated from the exergy exchange calculations they amount to 49 MW for a 20K temperature difference. 

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